Program To Randomly Select Numbers For A Bingo Caller - Prevent Reversed Numbers Being Selected

I have just about completed a .NET project to write a program to randomly select numbers for a Bingo caller. Over the last month or so Ive learned a lot about .NET but heres something that I consider to be odd and maybe one of you guys can offer an opinion.

One of the features of calling Bingo in a small local club is that callers often use little sayings to accompany certain numbers, I expect youve all heard of (say) All the sixes, clickety click for 66 or 5 and 9 the Brighton line for 59 etc. My little program gives an option to incorporate these with a prompt for the caller that can be edited outside of the program. One of these conventional sayings is used when a number is reversed 12 followed by 21 or 45 followed by 54 for example, when the caller might call (say) 1 and 2, one dozen, number 12 And the other way round 2 and 1, twenty one.

So, I programmed in a bit of code to detect this and to over-ride whatever might otherwise have been the quote with And the other way round and set about testing it. Ive been through literally dozens of full 90 calls watching for the occurrence of a reversed number, spent a few hours doing it, and not once has it occurred which is to say the least, unusual.

So, Im wondering about the Rand Function, could it be that it isnt possible for a reversed number to be selected? Just so you know, I randomly pre-select the order of all 90 numbers, I fill each of the 90 elements of an array with a random number first checking that the number selected hasnt already been stored, if it has, I just get the next random number (and check that too of course), but I cant see how that could prevent reversed numbers being selected, especially in light of the fact that frequently it's not the 'next' number that's used.