@Anne04 I just did another experiment. I used one of my T3 slips that come with values in box 21 52 and 53. If I delete the value in box 21 nothing changes what turbotax tells you you owe or get as refund. If you delete what is in 52 or 53 but leave the value in 21 the refund/owe value changes and if you delete both values in 52 and 53 and still leave the value in 21 intact the refund owe changes the most as it now counts both 52 and 53. From that it seems that turbotax counts based on what is in 52/53 not per se what is in 21.
Now that makes sense given how your physical Tslip defines what 21 is (the wording changed from last year to this year). Compare the wordings for yourself in your T3 physical slip for this year and last year describing box 21. However, that means that every T3 slip should have come with a value in 52 or 53 or both. But some T3 slips come with no value in 52/53 period. And Turbotax depends on an entry in 52/53 to flag the 21 amount. At least my turbotax
