I felt we needed greater clarification and wrote to our Chief Tournament Director of Africa Dr Magdy Mesdary and I am printing his reply verbatim:
If 1NT is opened occasionally with a singleton, then it is not a convention, as
long as partner is not aware of.
Ref. Law 40C - C1: A player may deviate from his side's announced understanding always provided that his partner has no more reason to be aware of the deviation than have the opponents. REPEATED DEVIATIONS LEAD TO IMPLICIT UNDERSTANDINGS, WHICH THEN FORM PART OF THE PARTNERSHIP'S METHODS AND MUST BE DISCLOSED IN ACCORDANCE WITH THE REGULATIONS GOVERNING DISCLOSURE OF SYSTEM. C2: Other than the above no player has any obligation to disclose to opponents that he has deviated from his announced methods".
So if it is a convention and partner is aware of and they have means to discover it , then it is a convention and has to be disclosed to the opponents; you may also disallow such convention if you decide to. However, if it is made occasionally without prior agreement then it can fire both ways, however, repeated deviation lead to implicit understandings which then form part of their methods.
I believe this certainly clarifies the use of 1nt with a singleton and as it is acceptable all over the world, I wish to confirm that we will continue to open such hands accordingly, without prejudice. However, I must reiterate that if it is used as part of your system it must be disclosed on your convention card and alerted at the table.
We will not longer be holding trials for the commonwealth Games as we have had a pair withdraw. Therefore the team that will represent South Africa is:
Larry Chemaly and Joe Israeli-Zindel
Krishna Malani and Ashok Samjee
Desiree Pieters and Nelonia Vorster
We wish them a great tournament and a safe journey to and from New Delhi,