There's a bit of confusion in this thread between (a) antiques, and (b) "curios or relics" (C&R).
For an antique, the status is determined by when the receiver was made, regardless of later alterations. Production of the 1896/11 Swiss Schmidt–Rubin receivers spanned the Jan. 1, 1899, cutoff date for antiques, and therefore some are antiques even though the guns were rebarreled and otherwise modified after that date.
Specifically, the original 1896 model was manufactured from 1895 through 1912, with serial numbers through 236,500 having been made before 1899. The alterations to the 1896/11 configuration were done between 1912 and 1920, but that's not relevant for this purpose.
If the gun thus meets the legal definition of an antique (that is, if the serial number is below 236,501), it retains that status even if, by mistake, some dealer required a Form 4473 to be filled out on its sale. Subsequent transfers can be made without any further formalities. The previous Form 4473 can be safely ignored. (But it's understandable that the dealer, given the serial number situation and out of an abundance of caution, asked for the Form 4473.)
On the other hand, a C&R (a gun made after 1898 but at least 50 years prior to the current date) has a different rule. It loses C&R status if substantial alterations were made more recently than 50 years prior to the current date. For example, if a WW2 gun was sporterized less than 50 years ago, it's not a C&R. In any case, C&Rs are treated as modern guns (requiring a Form 4473) unless the transferee has an 03 (C&R) FFL.
Incidentally, if the OP's gun is not an antique (based on the serial number), it's at least a C&R.