Old Texas Instruments Suffixes

Does anyone have a list of old suffixes for TI? Recently the 74HC154M chips we’ve received have been exhibiting behavior that they never did before-namely, melting off the boards when power is applied. This is happening over multiple units and boards. I would like to try a replacement made by another manufacturer, but I am struggling with equivalents, as no one seems to be able to tell me what the M suffix means. The current guide from TI doesn’t have a listing that makes sense. On the data sheet I see hints that it may relate to the package, but I’m not sure. Anyone know what M indicates in this case, and what a good substitute would be? Thanks in advance for the help!

CD RCA used the prefix of CD Texas instruments, Took over the line

M suffix is SOIC package

Excellent. I figured as much, but without anything official I wasn’t sure.