The AVA's Rules for Vaulting, Chapter I, Article 111, paragraph 7 requires that:

"Individual vaulters must wear a number which has been assigned to them by the AVA National Office. Number may be worn on the right arm or right leg and must be easily visible to the judge(s)." 

However since AVA National Office doesn't assign numbers to non-members and foreign vaulters, the management of each competition must assign equivalent numbers. The VoNW maintain a list of numbers we have assigned to our Canadian friends and reuse these numbers for each of our competitions.