Robin,
It is the letter I.
Not sure what you mean by 'Are you saying that there must be contact with the seal from the start once installed?'
What I was saying was that this particular seal that was supplied to do the job was MIS112 and the special support washer/spacer has a bevel on it that stops the lip deforming under pressure. Even if you find this seal, there is no guarantee the spacer lip will fit snugly against the seal. We found this out when one was demanded to repair a Ferret. The one supplied was marked MIS112 on it but the spacer would not face up to it. Investigations found this seal size also fits in a Land Rover front axle, but under another NATO stock number, so somewhere in the chain of supply an error occurred, there was a variation in the moulding and I seem to think there was a small mark or letter on the face to denote the correct one. If you were pedantic on fitting the washer, then the only way would be to machine one to suit an available seal. Using a seal with a dirt lip means there is no way the lip can be supported, it has to be a normal wiper seal, without dirt lip if you were to wish to utilise the support.
As I said, not done one lately and last time it was a correct seal.