My Apple IIc has a 342-0033-B "MON" ROM (aka "ROM 0"). I asked several people how it differs from the 342-0033-A, but nobody knew. I was advised to READ out the content with my T48 universal programmer, so I did. I then downloaded the 342-0033-A ROM from an online archive and compared both in Hex Fiend, which showed they are exactly the same!
No one seems to know what differentiates the A and B revisions, although some are now speculating it must be the chip model number. As you can see from my photo above, mine is a Signetics 27C256. But some revB chips have Apple markings on them like this:
In any case, I wanted to post this info as "FYI".
I also compiled the following info on all IIc ROM revisions, based on info I gleaned from around the web...
ROM FF (255)
"MON" IC: 342-0272, 16K: W1=closed, W2=open
(IIc Model: A2S4000, Apr'84 to Nov'85)
Slot 1 (Printer Port)
Slot 2 (Modem Port)
Slot 3 (80 Columns)
Slot 4 (Mouse)
ROM 0
"MON" IC: 342-0033-A & 342-0033-B, 32K: W1=cut, W2=soldered
(IIc Model: A2S4000, Nov'85 to Sep'86)
Slot 1 (Printer Port)
Slot 2 (Modem Port)
Slot 3 (80 Columns)
Slot 4 (Mouse)
Slot 7 (AppleTalk)
ROM 3 (IIc Model: A2S4100, Sep'86 to Jan'88)
"MON" IC: 342-0445-A, 32K: W1=cut, W2=soldered
Slot 1 (Printer Port)
Slot 2 (Modem Port)
Slot 3 (80 Columns)
Slot 7 (Mouse)
IIc RAM Expansion Card Support
ROM 4 (IIc Model: A2S4100, Jan'88 to Sep'88)
"MON" IC: 342-0445-B, 32K: W1=cut, W2=soldered
Same as ROM 3 but...
Improved RAM card firmware behavior when no extra RAM is installed
Fixed keyboard buffering bugs
ROM 5 (IIc Model: A2S4500, Sep'88 to Nov'90)
3.5" Floppy Drive Model
4MHz CPU Support