There are some tags which are both used to denote style and series at the same time, which makes it much too vague. (case in point: #131889 is clearly FiM (and mlp for that matter) based on series, and #131844 is clearly FiM (and mlp for that matter) based on style.
Proposal: Split these sort of tags into _(style) and _(series).
Alternate proposal: Remove all tags denoting style, since style is not always a unique identifier anyway. (else we would have a nezumi_(style), doug_winger_(style), gideon_(style) and etc...)
Updated by SnowWolf