If you use the wrong XDF, you usually get garbled maps, and/or values that make little to no sense.
If you modify a bin with the wrong XDF, you will likely be changing things that aren't what you think they are. You may not notice anything wrong, or you may get a corrupted bin that will cause a code 51 if inserted into the ECM.
Some maps and variables are in common locations and will show fine with the wrong XDF, especially closely related masks, that are used in the same ECM, but other things will have moved locations and/or have added/removed variables... so... Knowing you are using the right XDF is a little bit experience, and a little bit fining good resources for knowing what cars/engines use what XDF. There is also a byte in the BIN that will show you the mask, in most BINs (there are exceptions, like anything that is longer than 2 digits), but this byte can be in different places in different masks/BINs. Most are located at 0x08.
It's not possible to "lock" OBD1 GM BINs, however, some companies have gone as far as shifting the entire bin by a byte or two, and updating pointers to work correctly, or moving instructions and variables around to make it more difficult to know what has been changed in the BIN.
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