Could I suggest that the records may be sample pressings for copy matrices intended for issue in the UK - L.M. indicating 'London Matrix'
This is a guess as I do not have any proof as yet and do not know enough about the interrelationship between US Decca and UK Brunswick. Having skimmed through a number of titles I see that a decent number appeared on the UK Brunswick label after WWII, just when the industry here was beginning to re-establish the content of American material in its catalogues.
The other interesting thing about this group of pressings is they must surely have originated from one source and were pressed during a single time frame for a particular purpose - that a stack of such pressings were then discarded at one time and entered the same collection is also a logical outcome.