oh yes ... the sequence number is optional, but it makes it easier to
establish that there were no gaps in recording. Everything you need to
meet your requirement is in the ID and the timestamps.

The primary key is always the ID plus the sequence number - that way a
relationship that does not require "between" processing (ie a
relationship that is itself version.

This uses a fair bit of DASD, But at $1.00 per gigabyte, that's cheap
now days.