No. A Service Guide or certificate left blank is no indication of questionable provenance. Many collectors make a point of never having these papers filled in, since the receipt is proof enough and the entry matters in practice only where a guarantee claim arises. What decides authenticity is the pen itself, its finish, the engravings and the limitation number, not the completeness of the accompanying papers. Box and papers should nevertheless be kept, since they have a noticeable effect on resale value.
The Agatha Christie edition is a limited edition. Although a comparatively large number of pieces were made at the time, it is in lasting strong demand among collectors, and that is unlikely to change. An inherited example need not therefore sit unseen in a cupboard. Anyone putting a hitherto unused piece into service should be aware, though, that this reduces its collector value: unwritten examples with all their accessories fetch appreciably higher prices.