Targets for recruitment of markers have wobbled over a number of months and suddenly leapt to 9,420, up from a previously assured total of 8,800, which had a built-in 10 per cent contingency.
Mike Russell, SNP education spokesman, said: "The moving target leads to confusion."
But Bill Morton, SQA chief executive, replied that it was "a dynamic process" and targets changed as the authority received hard data from schools and colleges. Tis changed right up until the last minute.
A shortage of 1,184 markers for the main exams was confirmed on Wednesday, contrary to statements two weeks ago about positive responses from teachers and lecturers.
The shortage has forced Colin MacLean, the Scottish Executive's exam co-ordinator, to appeal to local authorities for schools to release staff from teaching duties to plug any marking gaps. The Executive will pay for supply cover.
Mr Morton assured MSPs that all papers will be marked by experienced staff. The authority needs more markers this year because of the increased number of courses at different Higher Still levels.