It is thought that January 1974 may be the last issue. Can anyone confirm this or otherwise?

This query probably arose from a problem that arose from one of the articles in this issue that resulted in a re-issue and possibly hastened the merger - details are being assembled.

See previous comment - information received - On the Point to Point page you ask "It is thought that January 1974 may be the last issue. Can anyone confirm this or otherwise?"
I believe that it was the last _complete_ issue, but that's not the whole story: because of the debacle resulting from Sosin's article in that issue, an apology was issued to Racal, with instructions to subscribers to "withdraw the existing edition ... totally from circulation" (See "The Great Marconi Mishap" in Radio Bygones #87 of Feb 2004). A few libraries did retain a copy though, eg the Bodleian in Oxford lists "two booklets" for 1974 (they have complete volumes for the earlier years). The second booklet is presumably the revised edition of Sosin's article and the accompanying table.

Additions to above comment:
As for Sosin's article, the non-Marconi receivers in his analysis were anonymised by assigning letters to them, but some were easily identifiable from their IFs, dimensions, etc. They included Racal's RA17L and their latest receiver, the RA1772. Unfortunately, not only were some of the relevant values in the table wrong, it was also asserted that receivers A & B failed to meet their specs. Those were both Racal receivers and Racal were understandably upset and called in the lawyers. The result was the withdrawal of the offending issue and a letter of apology that was circulated to all subscribers and also reproduced in the preface to a revised April 1974 edition of the Sosin article.