ID numbers for ancestors

Why have all of the ID numbers changed? it makes it very difficult to work with my uploaded GEDCOM file for CERT. It does not recognize any of my people inserted into my tree years ago.
Answers
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Person ID numbers may get changed over time due to Merges. Many people may have the same extended family they are still maintaining in older legacy genealogy programs. When moved from your source program (via GEDCOM) it is a snapshot of your tree at the instant of transfer.
FamilySearch is unique in that it is the only world wide FamilyTree of mankind. Additionally it is a living tree in that any and all can add and change people on the tree. When multiple people upload their GEDCOM files - at this point in time - most people and lines will already be out on the FamilyTree. That said, this creates the need to Merge these multiple duplicate entries.
As you note the unfortunate side effect is that you cannot expect the PID to remain the same; but by entering the old PID, the program will give you the option to go to the "Surviving Person". The good effect of this collaborative nature of FamilySearch - with crowd sourcing the genealogical research, most duplicate work is eliminated, and the overall work is sped up substantially.
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My understanding is that your CET is a completely separate tree, fully under your control, with completely separate data and identifiers from the main, long established, collaborative Family Tree. If you have specific questions about how best to copy data between the two, you're best using the specific Community Group on CETs, since that's where CET expertise sits.
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