Frensh ultralight registrations

[sutu5]

Looking through many frensh ultralight plane photos in Jetphotos database I recognised that there are two different ways their registration is stated.
One with the dash between the departrment number and the two or three letters and one without the dash.
Example:
with dash: 68-AIH https://www.jetphotos.com/photo/9470874
without dash: 28AJJ https://www.jetphotos.com/photo/10085760
On the airplanes themselfes I never could find a dash, but in various publications, i.e. AirBritain the dash is stated.
Does anyone know if the dash is part of the registeation in official frensh register?
Yes I know the dash is only a small and for the most of us, including me, an irrelevant detail, but I think in a database where we want find an enty, a uniform representation would be desirable.

The second issue with frensh ultralight aircraft is that many of them has two registrations. One as discribed above (departement mumber followed by two or three letters) and the other a regular F-reg (F-JAAA to F-JXXX).
For this I found the following example:
01-ABJ / F-JTHR : https://www.jetphotos.com/photo/10570447
I guess the "regional reg" is painted under the wing. But is it realy clever to list this plane with the registration that is not visible.
I am longing to know how you (photographers & admins) see these points.

Greets Felix

[JuklicekCZ]

I've found some nice discussions that might help you.
https://www.pprune.org/archive/index.php/t-368485.html
I understand it that the F-number is just a callsign for ultralights, not the actual A/C registration.

[bleuair]

Hi Felix,

a) on the dash, I would go for the "with dash" version. It is easier to read. Though the letters on the aircraft are not including a dash in every case. Your example 01-ABJ is "dash-less" under the wing (I know because... ).

b) The registration is the 01-ABJ. Every uploader who has access to the plane or to web sources should have a quick look under the wing (and the data plate in case of static access). Good practice and helps improve the data consistency. Every aircraft showing a F-Jxxx reg. MUST HAVE a proper registration somewhere. The radio call, the F-Jxxx identifier, should not be used unless it is completely impossible to establish the correct rego. And yes it happened to me before that I had to search the web AF until I got to the correct rego which I forgot to check on the plane...

Thanks for your contribution!