scourgify:

• only the first 20 tags apply for tumblr.com/search/tag 
  
• the rest are not picked up
• beyond 20 tags - they only show up on yourblog.com/search/tag 
• they also don’t show up in yourblog.com/tagged/tag 

so if you want to tag people in stuff, beyond 20 tags is useless 

and for your tag system, if you’re a tag rambler like me but still want to tag stuff for organisation, be sure to have those tags somewhere within the first 20 tags