Time Machine - does it work?

hi, got question, time concerning time machine.. have fw disk connected imac , hade set time machine use disk..everything worked fine, until...
doing changes in settings , tried menu in time machine settings named "select disk" - well, there selected same disk had been used before (that external fwe disk), left menu, in main tm setting windows saw: oldest backup - never, latest backup - never, next - in few seconds..
shocked me (before entered select disk menu, there dates oldest backup , latest backup), after new backup performed, again there ws date of first backup - so, can sure nothing changed , time machine working ok (having backups made ready? backing now?)

can enter tm , on timeline see first backup, can see others... means works? or have format external disk , set time machine again properly?

thx.

 

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