Yes, you're right, I did not think that specifying a limit to 3 would work properly in this case, and it does, but, as you said, it still won't work in the case of ABC:

$ perl -E ' say map { qq{"$_"\t}}  split /(\d+)/, $_, 3 for qw[ AB23C 
+ABC23 23BC ABC ]'
"AB"    "23"    "C"
"ABC"   "23"    ""
""      "23"    "BC"
"ABC"
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