I have no idea (or really that much interest) in just how many pieces this, that or the other performer may have, or claim to have, in his/her repertoire but I do think it important that any consideration of - or claims in respect of - anyone's repertoire extent need to be taken alongside what is supposedly meant by "having" x number of pieces in the repertoire. In one sense, it may be that it is only reasonable to claim to "have" certain pieces in one's repertoire if one has them in it here and now; some performers may have played certain pieces once only and then never touched them again in many years - would those pieces count? Another factor is the extent to which performers can learn pieces rapidly to an acceptable public performance standard. Leslie Howard is a distinguished Liszt scholar who has indeed recorded just about every known note that Liszt wrote for the piano and, of course, he also has a considerable amount of music by other composers in his repertoire. Have a look, however, at the repertoire claimed by Ian Pace on his website - and then consider the colossal repertoire of John Ogdon (who, had he lived, would have reached 70 next week); John's rate of absorption of music was truly phenomenal - he could not so much just play all kinds of challenging music at sight but actually perform it at sight - in other words, he seemed able to make interpretative decisions without apparently having the physical time that most normal mortals would usually need in which to make them.
Best,
Alistair