I'm sure if you did a change of particulars which was changing anything which would have affected VRT at first registration then you'd probably be liable for any extra VRT owed. I wonder are any of these discrepancies back handers or favours done so that VRT would be cheaper?
I know when I VRTed my e34 some years ago there was a difference of a few quid on the different drop downs. I went for the cheaper option at the time if I remember correctly. Now my e34 wasn't expensive to VRT but I'm sure there would be many cars where a dealer could make a saving by registering cars incorrectly.
From what I have gleaned though some adverts and post in various Irish forums a lot of e63 650i when new were "accidentally" registered as 3.0L cars not as 4.4L cars. $400 a year savings in tax so yes, it has been taken advantage of...
Here's an example of one such car:
http://www.bmw-driver.net/forum/showthread.php?t=59473
(e63 650i being referred to here also in post #50;' http://www.boards.ie/vbulletin/showt...7395210&page=4)
I seem to recall a Z4M roadster (blue, iirc) knocking around for a long time with the same "problem", a 3.0 engine on the reg doc. Grand for the purposes of road tax, but a pita in the form of a shadow over the car as regards exporting it to the UK when it couldn't be given away here a few years ago.
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Current: BMW 530e M-Sport - '17, BMW 630i Sport auto - '07, BMW 325i Coupe - '93, BMW Z4 2.5si Auto - '07, '90 BMW 316i Lux.
Previous: BMW 328i Coupe - '96, BMW 530i SE auto - '07, BMW 530i Sport auto - '02, BMW 318i SE Touring - '07, BMW 330Ci Sport - '04, BMW 520d SE - '11, BMW 523i SE - '00, BMW 328i SE Touring - '00, BMW 523i SE - '97, BMW 323i SE - '98, 330Ci - '00, 325i Coupe - '93, 318Ci - '01, 316iSE - '98, 325iSE 2dr - '91, 320i Conv - '91, 325i Coupe - '92, 320i 2dr - '91.