Other mistake: At the start of the line dancing scene where Ray Von is deejaying, if you have the subtitles on, it says the song is Hillbilly Rock, Hillbilly Roll by the Woolpackers. It's actually 5,6,7,8 by Steps. (I'm quite embarrassed I know that).
Other mistake: How come not one single person at the Phoenix Club knew Max's surname, namely Bygraves, during his time as a doorman? This only came to light in the "Road to Nowhere" spin off.
Chosen answer: He doesn't have a longer name eg. Dennis or Denzel it's simply Den. Brian simply says this to make Den annoyed by giving him a long name. Another theory is Brian is so stupid that he just doesn't know Mr. Perry's name or is unsure of it but I'm sure it's the first one.