Create a table called source. In that table make the records have a numeric value tied to each source. 1 = API 2 = form and 3 = grid. Place the related lookup field inside of your record form where you are wanting to track how these came in. Now when they do the api edit record call add their field ID to the call and the number is value 1 to be sent over. Same with the form. And with grid edit just make an action or automation that basically states if it comes in without a source then write grid edit in source, since you only have 3 options and the other 2 are taken care of.
There is probably a simpler way, but this way would be 100% automated.
