While this link says nothing about 20MPH doesn't mean it still isn't part of the law. But this is a direct qoute from your link.
"The vehicle must be used exclusively for exhibitions, club activities, parades or other functions of public interest. Vehicles displaying Antique plates may not be used for regular transportation or carry advertising. The vehicle may be driven to and from a location for routine maintenance."
That buddy is the definition of a parade vehicle. Right from your link.
You left out the first sentence of the reg. It clearly states that A.P.s are issued for (vehicles) that are at least 25 yrs old and are collector items. Then it goes on to say (above) that A.P. vehicles can only be used
exclusively for certain activities. Parades are parades. Simple enough. Exhibitions, club activities and other functions of public interest cannot and should not be defined as narrowly as you did as parades. Those activities include lots of other stuff...off road runs, car shows, rallies, roundups etc. You could argue that in any forum anywhere and win.
And please point me to "part of the law" that states A.P. licensed vehicles can only be driven 20 mph or less. I guess if such a law exists somewhere and is written and posted, all us A.P. licensed vehicle owners now have to reduce our speed to 20mph or below. Ludicrous...we'll get ticketed for violating the minimum speed law or get run over by a semi-rig.