My version of Keil Assembler Documentation states as follows:

However the test I ran as described in the previous post seems to prove this wrong.

I suspect that Keil allows the A51 labels to be longer than they state in their documentation because if you use their companion C compiler there are many compiler generated labels that are produced by taking the users source code labels and adding various prefixes and suffixes. This would seem particularly important if you were using the #pragma SRC directive in a C source file that then produces an A51 source file which you subsequently expect to assemble with A51.

Michael Karas