Flight deck "access" and "use of jumpseat" are different. Broadbrush rules swept in after 9-11. Interpretation rule-bending became the norm.
Long time ago, Pushy Exec demanded use of a FD jumpseat. Reluctant Capt had heart attack just before V1. FO controlled, stopped, got the Skip to Hospital and gave the Exec a full debrief !
The Company DFO ruled that the Flight deck jump seats were no longer to be used as "an extention of the cabin". Good decision, no messing and we all supported.
"Access" is another matter and we all now what happened after 9-11.
Glory days are well over. I was granted many FD visits as a kid during summer holls. After a long visit, super MEA Viscount Skipper let me stay for landing & gave me a pair of MEA wings. I was 6.
As a Crew rostering clerk, I pursuaded many Captains to allow me a FD trip (most days off). One empty leg return to Gatters, Chief Pilot of the airline put me in his seat, RHS was a Senior Capt, Flight Engineer. I flew the big beast (Trainee PPL, 3 hours on Bolkow Junior) until girls down the back complained of being sick..
Decades on. Lots of lessons on. Most could see sense in complying with black & white Company procedures. Few would "nudge, nudge-wink,wink" and bend the rules eh ? Depends how pretty they are, I guess.