If I was being cynical then I might suggest that when Montblanc decided to issue the 147 Traveller, they then made all of the resin parts for the 146 and 147 from the same moulds, so that they became identical and they wouldn't have two same girth pens with different sized caps and barrels.
In that scenario the previous 146 that is slightly different, has to have been made before Montblanc introduced the 147 Traveller. You might be able to get close to the issue date if it has a different feed and monotone nib. If it has a serial number then I believe they started in 1991.
Try typing "Montblanc 146 dating chart" into Google and see what comes up.
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