this looked strange to me (even as a SE) and I tried to find an 2013 price file... finally I found one in a temp folder in an old backup
So MSRP price list wise we had back in 2013 CPU Tiers.... Tier A 1-6 Core; Tier B 7-12 Core and Tier C 13-18 Cores. This concept was changed to CPU Socket licensing without Tiers later.
Comparing this with the actual price list (as well MSRP list prices) ...
Maintenance (9x5) Tier A Enterprise Jan2013 to Enterprise Aug2016 is 1,26 times (I would say that this is in the Industry Standard range... and think about at that time everybody used 4 Core CPUs while they are using today 10Core CPU with much more VMs per CPU)
Maintenance (9x5) Tier B and Tier C Maintenance Jan2013 was even more expensive then today. Veeam used the Tier A prices later as base when we introduced socket only licensing.
Maintenance (9x5) Tier A Enterprise to Enterprise Plus is 2,01 times and this comes from the fact that Entperprice Plus edition has a much higher price while delivering more value (see above). As Customer you got the new edition for free without payment.
Btw. Maintenance (9x5) Tier C Enterprise Jan2013 to Enterprise Plus Aug2016 is nearly the same price.
I work for Veeam EMEA and maybe other countries have other price lists. Maybe you got a special discount in 2013, upgrade from (9x5) to (24x7) or used a promo or....
Contact a Field SE from your region an let him see the quotes and invoices, he will find out why it is that high compared with 2013. If you PM me your email address we can figure it out together if you like.