For early timestamp with timezones, postgres gives odd offsets, for example:

select timestamp with time zone '0005-02-03 10:00:00.000Z'

gives "0005-02-03 10:53:28+00:53:28" on a server in Germany and "0005-02-03 10:53:28+00:53:28" for a server in the UK. Weird!

I guess these are based on your environment's locally stored timezone file. This isn't part of the spec but postgres does output it, so I guess this project should handle it.

I'll submit a PR in a moment.