Well to my knowledge, you can't get any of the cars that have no year entered via the Birthday Tickets so it's more accurate and probably for the best to leave it blank. If you add the year you'll get people wondering and maybe even asking you, why they can't get a particular car via the Birthday ticket for that year.
Indeed. The search in mygranturismo.net database when you click on a Birthday Ticket (clickable on "my Page" once marked as own on the items page) is done on a different field than the year displayed in car list (which is a "Year Estimated").
For advanced users, here's a complete list of accessible fields (some previously undocumented) through url editing on
carlist.php?param1=value1¶m2=value2&...
that I sent to a user who asked for it a few weeks ago, and that I've defined for internal use at first, but that can be used to build url to share a very specific list of cars (see set/unset for fine editing) :
level=##
drive=[ FR | 4WD | ...]
quality=[ P | S ]
rm=[ y | n ]
make=#makerid#
bonus=[ y | n ]
trade=[ y | n ]
body=Xxxxxx // This field is often empty in DB, but it may give result with Xxxxx like NSX or R8... result not garanteed
set=###,###,### ... // A list of car's ID as values. This allow to build a custom list of cars.
unset=###,###,### ... // Given car's ID are removed from the result. It must be used in combination with another filter.
zone=[ Europe | America | Asia ]
country=[ USA | UK | Japan | France ... ] // This can be access by a click on the "my Page" garage stats.
year=#### // Shows only cars from this EXPLICIT Year (cars with no Year in the game can't be seen)
year_est=#### // Shows only cars from this ESTIMATED Year (Estimation can be wrong for some cars, but every cars appears here)
min_year=#### // Shows only cars with ESTIMATED Year from this one and above
max_year=#### // Shows only cars with ESTIMATED Year from this one and below
max_price=####### // Shows only cars equal or below that price. Based on old (prior to 2011/03/24) "price" field and not the new "price @ 0km'
max_kg=####
max_ps=#### // a max Power filter that it is good to avoid using because of the ingame variation for a given car.
avg_wkg=#### // Shows cars that currently have +/- 6% of the same Power/Weight ratio. This filter may be "built" in a smart way by using
http://www.mygranturismo.net/tools.php page.
garage=[ y | n | #userid# ] // Note that if a userid is passed here, the Own button in left column still shows YOUR cars.
Additionally, you can order on one of the following fields :
order=[ year_est | pp_ini | level | power | weight_kg | torque | kw_per_g | price_0km | price | maker | pp | model | P | rarity ]