what you are requesting is impossible, you are requesting allowance be made for your prior experience and circumstances with regards your crossover ... i dont know you, you may be the worlds most competant diver or a complete f**kwit, and thus the agencies have introduced standards to eliminate the need for me to means test every diver who enters my establishment, you either have the prerequisites or you dont. if you dont then we dont even need to get wet!
look at it this way, you might be the most competant diver in the world and be a "good lad" but your not the problem...its your family! thats who a dive operator needs to worry about...
lets go down this scenario..say you do a mixed gas dive in a cave with minimum crossover time as we have decided in your case things were "nearly" the same, and heaven forbid you have a disaster, your insurance company (which incidentaly, having a lack of isn't something to brag about, especially if your preceding breathe lamented the fact you dive uncertified with mixed gas, it doesn't show a responsible approach to CCR diving for some of the nexcomers
...enough ill save that for a different thread)..any way your insurance company will see a hole due to lack of cave training and possibly due to minimal crossover training, and please remember this is hypothetical, whether i agree with it or not is irrelivant, but the bottom line is they wont pay! and will probably say... "sorry mrs X no money for you" mrs X wont think,"oh what a tragedy i'll miss him! but weren't the boys down the local dive centre good lads by allowing Mr X to commit to this dive, i must buy them a crate of beer," she will probably think "where am i going to find X juniors college money!" and will go after the dive centre legally.
and in the court one of the first questions will be...how "nearly the same" were these units?... unfortunately you who thought they were "very much the same" and would possibly put forward a good case, aren't around!
So you might agree if you were in the dive centres position, lack of certification means no gas and maybe no cave diving, so you need a crossover and if you were the agency, you would agree a standard needs to cover EVERYONE in one fell swoop, and this always means "overkill" for the diver with good skill retention.
either way you would probably go next door to a centre that "turns a blind eye", and in turn i would lose your custom, but on the otherhand i thankfully lose the potential of having my pants pulled down and being anally raped by Mrs X's law team.