This recent news from the UK suggests we may want to call it the Waterstones Apostrophe. Seriously, though...

It could be argued that in some cases omitting the apostrophe is just fine. Each of the three cases below has a perfectly grammatical interpretation with the same meaning: there is a manual and it has to do with students.

1 Student's Manual (N-gen N) = possessor - possessed noun
2 Student Manual (N N) = attributive noun - modified noun
3 Students Manual (N-pl N) = attributive noun - modified noun

Not that the use of the genitive 's in (1) is not truly a possessive relationship anyway. Also, since the manual is intended for use by one or more students, the use of either the singular of plural of the attributive adjunct student in (2) and (3) could be well-motivated.

So the Waterstones Apostrophe isn't as much of a problem as the Greengrocer's. This is probably why there is no commonly accepted name for it.

Hm, perhaps there is one common exception:

Also found with "MENS". Of course neither MENS nor WOMENS is a proper word. So we might also call this the Restroom Apostrophe.

This recent news from the UK suggests we may want to call it the Waterstones Apostrophe. Seriously, though...

It could be argued that in some cases omitting the apostrophe is just fine. Each of the three cases below has a perfectly grammatical interpretation with the same meaning: there is a manual and it has to do with students.

1 Student's Manual (N-gen N) = possessor - possessed noun
2 Student Manual (N N) = attributive noun - modified noun
3 Students Manual (N-pl N) = attributive noun - modified noun

Note that the use of the genitive 's in (1) is not truly a possessive relationship anyway. Also, since the manual is intended for use by one or more students, the use of either the singular of plural of the attributive adjunct student in (2) and (3) could be well-motivated.

So the Waterstones Apostrophe isn't as much of a problem as the Greengrocer's. This is probably why there is no commonly accepted name for it.

Hm, perhaps there is one common exception:

Also found with "MENS". Of course neither MENS nor WOMENS is a proper word. So we might also call this the Restroom Apostrophe.