Club Log maintains a JSON file containing a list of all Club Log users' callsigns, with additional data from LoTW about their last-known uploads.

You can access this file here:

Inside the file, you will find a JSON array of callsigns. Each callsign has array key-values of known information. All of the possible array keys are listed below:

firstqso = The date and time of the first QSO in the log

lastqso = The date and time of the last QSO in the log

lastupload = The date and time of the last upload made to this log

locator = The 6-character Maidenhead locator of this user (useful because this is manually set by the user, and not guessed)

oqrs = boolean true if this callsign has Club Log OQRS enabled, otherwise false

last-lotw = The last QSO date and time in LoTW for this callsign.

If a value is not known (for example, a user has never uploaded) then that array key is not included. This is to help keep the file size a little smaller. At the time of writing, the ZIP file is about 2MB.

 For example, here is the start of the report today:

{"1A0C":{"firstqso":"2012-07-01 06:25:58","lastqso":"2012-07-05 05:46:42","locator":"JN61FV","oqrs":false,"last-lotw":"2016-04-23 20:15:52"},"1A0C_14":{"firstqso":"2014-12-28 08:19:56","lastqso":"2015-01-06 10:23:26","lastupload":"2015-01-06 16:23:44","locator":"JN61FV","oqrs":false},...etc...}

The LoTW information is derived from this file, provided by LoTW:

If you only want LoTW information then you may find getting this file directly is more suitable, but the report provided by Club Log is smaller and in practice is generally faster to download. 

This file is updated every 7 days.