The date should change! I agree it's odd you have two of the same movements exhibiting the same behaviour but one of the reasons I'm replying is that I'm working on an AS 2063 based watch where both the watch and a spare 2063 have the same problem of the quickset not working! Maybe this AS series has some inherent fragility around the date change mech in general? Anyway it looks like you have little choice but to tackle the dial side and investigate the mech. This is a useful photo ... https://watchguy.co.uk/cgi-bin/media?image=P1030810.JPG&email=&wat_id=2180 ... and you'll primarily need to monitor the operation of the date change device (bottom left in the photo) to check it is pushing the date forward.

It didn't look like there was additional room in the barrel. Also, the barrel cover is thicker in the middle than it is on the edge so it would almost certainly make contact with a 3.0 mm mainspring.

what was bothering me in the back of my mind is I worked on a ball watch and there were some differences and I just can't remember what they were? then before you remove the mainspring did it seem like there was additional space in the barrel for something wider? It's unlikely that they made a custom mainspring for the watch so it would have to be one of the Hamilton mainsprings. so I'm giving you the complete Hamilton 16 size section so you can see what once was available and what is currently available hopefully.

Hi everyone!  So I recently pick up a Bulova Set-O-Matic with a AS-2066 movement.  The watch was not working when I got it but after a cleaning everything seems to be working great.  The only issue I’m having is that the date does not seem to switch when the watch passes 12 o clock.  The day of the week changes just fine when passing 12 o clock.  When I manually set the hands past 12 still no luck.  The only way I can change the date is by the quick set feature.  I came across a second AS-2066 that also does this.  Is it coincidence that they both do it or is it by design?  Any thoughts would be greatly appreciated!

I don't think the 534B will work because it has a width of 3.0mm whereas the broken mainspring measured 2.82 mm. The 534-718047 with a 2.80mm width is the one I've been considering and should work if the shorter length is not a problem.