I do not think, therefore, that it will help your appeal case much to argue this point. However, I am quite ready to be corrected if others think differently.
Like Alex, I am doubtful about this. Strictly speaking, you would have to show not only that the authority had made a mistake in its admission arrangements, but that you were therefore denied a place to which you would otherwise have been entitled
. Whether or not you have been denied a place for this reason seems somewhat speculative.
The current code of practice has no legal force (LAs should "have regard to it"), and it is not clear to me whether an Adjudicator has ever made any ruling on this matter in relation to Lincolnshire.
I think you could quite reasonably ask the IAP to consider whether the admission arrangements have been properly applied, bearing in mind section 7.3 of the current code of practice, but I would then move swiftly on and focus on your case for prejudice.