In England, the majority of people take GCSEs with a variety of different exam boards and then move onto A levels with a variety of different exam boards which are often not the same as the board(s) they took the GCSE in. It is virtually unheard of for someone to do all their GCSEs and A levels with the same board. Abroad it is slightly different, and there is a bigger gap between Edexcel IAL and CAIE, but it still shouldn't cause a problem.