Club Log applies the official rules of ARRL's DXCC award scheme exactly, using its extensive knowledgebase of exceptional callsigns and historical operations that either have or have not been accepted for DXCC to validate the QSOs in your log. Once you upload your log to Club Log, Club Log will check and then count the valid DXCCs you have worked and may have confirmed, and display the counts on its log reports and league tables. 

Hopefully Club Log's DXCC numbers are identical to the statistics reported by your logging software, but if there are discrepancies you can investigate and resolve them as follows:

The DXCC count is slightly wrong

If a small discrepancy is found, check the email that Club Log sent you after you uploaded your log. Did Club Log report any warnings or errors, perhaps rejecting some of the QSOs you claimed?  If so, the email report is a good clue about the reason for the discrepancy.

Various DXCC errors crop up repeatedly due to limitations of some logging programs (e.g. routinely identifying KH7 calls as Kure Island, whereas most are on Hawaii) and out-of-date country files. Jim AD1C updates the country files several times a year, so it's always a good idea to grab the latest version off the web, update your logging software, and re-check the calls in question.

To check further, use the Log inspector to check Club Log's analysis against your logging software. Look up a DXCC country or callsign that you are sure you have worked but is not showing up in the reports. Does Club Log map it to the same DXCC country as your logging program? Double-check that the date of the QSO is within any stated range. Check the notes. If Club Log says the QSO is "Invalid", check your ADIF closely (remember that the ADIF you upload is the only source of all the information you see).

Don't forget that QSOs with DXpeditions are usually only valid for the DXCC concerned within the specific dates and times of the operation: if you log QSOs outside of that strict range, Club Log (and the DXCC desk) will normally reject them. A common reason is that dates have been recorded or transcribed wrongly (typically the days and months have been swapped, or the QSOs were logged in local time instead of UTC).

If you expect to see a QSO confirmed, but it is only marked as worked, remember to check your ADIF. If that doesn't show a QSL_RCVD=Y or an LOTW_RCVD=Y, it will not be credited in Club Log.

Other sources worth researching for information are, various DX news sites, and Google.  If you logged a dubious QSO with a rare DXCC fairly recently, it's worth checking back on DXcluster to see whether the call was spotted around that time. Often you will find a similar but slightly different call was spotted, implying that you (or the DX operator!) probably made a simple mistake in sending and logging the QSO.

At the end of the process, if you remain convinced that you are correct but Club Log is wrong about a given QSO, go here for further advice. Please only approach the Helpdesk if you have exhausted other avenues.

The DXCC count is completely wrong
If the DXCC counts in Club Log are significantly inaccurate, use the Log inspector or Call tester tools to check a few calls for countries that you know you have worked but are not showing in Club Log. You will probably find they have been mapped to "Invalid". In extreme cases, you might find that all of your QSOs are invalid!

The reason for this is that the ADIF uploaded has claimed a DXCC value of 0 (zero), or a QSL_RCVD status of "I" (meaning invalid). These are both accepted ways to mark a QSO claim as invalid in ADIF files. Some logging software invalidates everything! Club Log doesn't report these as errors in your upload since this is the proper way to invalidate QSOs.

ADIF is a plain text file format so you can check and if necessary edit an ADIF file using an ordinary text editor such as Notepad or TED (an excellent bit of freeware, by the way, available for both Linux and Windows). 

Here's a typical ADIF record in a file downloaded from LoTW (line numbers and the green line have been added by the help desk software):  

The text between angle brackets is the field definition consisting of a field name (according to the ADIF standard), a colon separator, and the data length in characters. The text that follows is the data value for that field. Depending on how it was generated, your ADIF file may well contain different fields, or list them in a different order.  It may use a different letter case. It will certainly contain different QSO data of course.

For example, if you are looking for a QSO with G7VJR which is missing or invalidated in Club Log, search the ADIF file for "G7VJR" using the text editor's search function until you find the QSO record you're looking for. 

Does it have a DXCC value of zero, or a QSL status of "I" for Invalid?  Does it state that the DXCC country code field is 3 characters long, but in fact the data is just 2 digits?  Does it end with an <eor> or <EOR> end-of-record marker?

Once you have identified a problem in your ADIF, you could simply correct the error and re-upload the ADIF to Club Log ... but that will not solve the original problem. It is much better to correct your original log so that the next time you happen to do an ADIF log export and upload to Club Log, the error will not come back to haunt you.

If it's not immediately obvious how to correct the log in your logging software, check the embedded help or get support from the supplier of your logging program. All loggers allow users to edit callsigns, dates, modes, bands/frequencies, QSL and LoTW status etc. manually, or at least to delete and re-enter QSOs. Most also allow users to change the DXCC countries allocated to QSOs in the log, using either the numeric country code or the name of the DXCC entity.

Please don't ask the Helpdesk for help until you have checked your ADIF file with care.