"If birds descended from dinosaurs, we would expect
the same 1, 2 and 3 pattern,"
...and that's indeed what we find. What Feduccia & friends call the "thumb"
is the prepollex, and "Element X" is the 5th digital ray. I'll dig up the
references later... or do it yourself, they've all been discussed in the
archives.
While probably not impossible (see kiwi fingers), the frameshift hypothesis
is simply unnecessary.