I have purchased several batches of Morrowind furniture plans. I buy 50 at a time and check how many new ones i learn and how many were old duplicates.
The new voucher merchant documents seem to have (not necessarily accurate):
- 119 purple plans.
- 63 blue plans.
300 purple and 200 blue random documents from the voucher vendor left just a handful of Morrowind recipes to purhase for complete collection. The purples costed 15000 vouchers and blues 4000.
Looking into numbers, e.g. 300 purple plans gave this time 94% of plans. 150 plans gave 70% of plans. At some point it’s better to stop buying documents and just buy the last ones from guild vendors.
The other half is that duplicates are sellable. You need to purchase the same amount of documents as there are unique plans, sell the duplicates and buy the unknown plans to break even in gold. This is if course assuming you find all missing ones and can sell dups. This will cost about 8000 vouchers.
See also drop rates in PTS.