It's correct as written. Where necessary here means in those places that it was necessary.
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AnonymousMy poor parsing is like this: Citations which(that) are neccessary.I think that's where you went wrong. It's not the citations which are necessary; it's the updating that may be necessary, depending on the citation.
Anonymousin those places that it was necessary"that" ~ "where" ~ "in which"
CalifJimI think that's where you went wrongIt goes to the heart of the issue.
CalifJim"where necessary" = "in any case [where / for which] updating was necessary"The parsing is clear to understand. I'd think of "where necessary" as a fixed phrase
AnonymousI'd think of "where necessary" as a fixed phraseA wise decision.
CalifJimLess formally, 'that' can substitute for 'where'.Oh my, I do not know the first thing about it.
AnonymousCalifJim Less formally, 'that' can substitute for 'where'.... in that sentence. This is an explanation of why BlueJay used 'that' in that sentence. It is not a general rule that 'that' can substitute for 'where'. In the five sentences you wrote as examples, the ones with 'that' (#3 and #5) are not correct.