I know many brand dont have any certification but still have great accuracy but you can have hit and miss. One such example that burn me was VC. While most of their watch are well regulated They officially do not guarantee better then 8 sec per day which is shameful IMHO. I got a piece from them that ran 8sec / day and even 10 sec/day in some position and they refused to adjust it (even my Panerai runs 3 sec/day or less). Needless to say I unfortunately sold that VC and will probably never buy another one