My understanding is the intention of the NOTAM is to advise operators not to use MAN as a flight plan alternate.
MAN has continued to accept diversions on the day where resources allow - it has continued to always accept emergency diversions.
There are very real stand shortages at peak times and throughout 24/7 there are Resource shortages across all departments/service partners.
There is a regular check of both stand, MAG , handling agent resources etc and the airport community is updated on this.
The staff in place each day are generally making a huge effort across companies/departments to support just the planned operation.
When considering (for example) a "splash & go" diversion it really won't work if the fueller makes clear it hasn't got the resources to fuel before the crew go out of hours.