You should review part 330, https://www.fdic.gov/regulations/laws/rules/2000-5400.html#fdic2000part330
The FDIC wants a signature card but does not define what one is, or what it is not. It does want, but again is not required, the type of account, single, joint, etc. So having an original form and amendments will be fine. The difficulty comes in when one or more of those amendments cannot be found on that 15 year old account after a merger and those employees are retired who handled those. The point is, the more items that comprise your signature card for an account, the greater the chance of an error.