Many thanks again for your quick and comprehensive reply.
I have never seen a Will dated in this manner before and, to me, it appears quite odd to include details of a reigning monarch within the text especially to add to a date.
Thanks for confirming the the addition is the 'proving' of the Will. It looked that way to me but I have no knowledge of Latin and needed the assurance.
The fact that this, and one or two other Wills I have looked at, have little or no punctuation does cause me some difficulty in interpretation at times. In the case you mention it is possible to read the text (now I have had help!) two ways. However, I have the advantage others haven't of the full text and given the mention of both a farm at Birdham and property in Chichester it does seem likely you are right about it being four rather than three words.
Once again, many thanks for your help.