Well, guess what, your luck hasn't changed, YET. (^_^)TX began keeping vital records in 1903, andEverton's Handybook for Genealogists shows Cass Co, TX has birth records beginning 1903.Now, there is always the chance he applied for a delayed birth certificate.And, when all else fails, you might find some kind soul who will go to the courthouse and check those records for you.They often are filed separately from "regular" births, and clerks don't always think to tell you about them.
You don't say when Paul died.Did he live long enough to have applied for a Soc Sec card?Did his death certificate give his SS number?If he died prior to 1963 he won't show up on the SSDI, but that doesn't mean he didn't have a SS card.If he had a SS number, he would have filled out the application for that Soc Sec card, and that application should show the names of his parents. Hang in there!!