That last Joe Glaser letter starts a bit strangely. "Just getting around to answering my mail and found your letter of August 8th ..." 
 
We've seen that there were, at least, two Joe Glaser signatures. The guy must have had people working or him. He (or ABC) had a bunch of different musicians to manage, including Brubeck and Ellington. But this - and much of the other correspondence - is written as if he's a one man band.  
 
Now he clearly did have a personal relationship with George A - discussion of TV programmes and other stuff in those letters shows that - and you could expect some of this correspondence to be dealt with by Joe personally. But there are routine business letters in this lot. They seem to be signed by someone who writes Glaser with a capital G that looks like a capital G (even though there are interesting bits in them that seem to go beyond strict business, no doubt his staff knew the sort of thing Joe would put in a letter, perhaps he had even said to mention such and such). The letters in which one feels that Glaser is really speaking (eg 3 July - "George, I definitely and positively will not accept...") are signed by someone whose capital G's look like capital S's and I reckon those are Joe's own signatures. 
 
MG