Cheers to your active and friendly presence here, Sweets!
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Concerning the numbers:
23377 IS Jan64 (this is a TL), as it is the numerical representation of Jan 01, 1964 in Excel.
42339 stands for Dec 01, 2015. December1 translates to it.
Excel does the auto-transformation of the names to the numbers as soon as they are entered into a cell (a major peeve for me, as different formats between English and German play havoc too often).
The only chance to overcome the problem at hand is to preface those (or all) names with a ' (apostrophe) BEFORE ENTERING to Excel to eliminate the automatic transformation.