I never knew that....we moved to Spain in 2004, no job, no income ( at the time ) and not of pensionable age but had properties in both countries. We weren't asked, nor did we tell about monies and savings, we just packed up, went and moved in. We had no NIE ( their national insurance number) I used my driving licence number initially when asked and at the time we were no where near self supporting. When we asked about taxation and payments both our bank manager and solicitor basically shrugged their shoulders and implied that we didn't even ' join the system '.....We basically swanned in, stayed for 8 years, sold up and swanned back out again.
We weren't alone either but I would imagine that things have tightened up since then.