Reversed Perec (fr)?

I do not remember a discussion about the R18, I do not remember/know who has set these codes, I am not sure I did that myself (I did it for the recent ones when I found that list of codes).

/!\ Always the same old story of Renault codes! /!\

I was wondering how a car unveiled in 1978 (the Renault 18) could have a post-1979 project code (X34) in the IMCDb? Shouldn't this car have a R134 code for the sedan, R135 for the Break/SW/Estate? With a fourth digit or letter if the exact model is known, of course.

Even the planeterenault.com list gives these 2 codes, and its "new system" X34 mention is just the X one (="accepted project, soon to be manufactured") without any L (sedan) nor K (Break/SW/Estate) complement.
Web searches on "Renault R134" often give Renault 18 related links (DuckDuckGo, Bing, Ggle...)⁽¹⁾

Was it a discussed choice of the admin team, or could it just be an early error while reading the technical data of the car (errare imcdbum est )?

By the way, it seems that no Renault Fuego has a code (but I didn't check all the pages). According to the preceding 2 sites, it was R136.
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(1): and the searches with "Renault X34" give... some IMCDb links at first and almost all IMCDb pictures of Renault 18 (at least with DDG and Bing)