[Nebulosa]

I will try to reply, but I'm not 100% sure.

have they simply not done bonitation (yet?) or is the data just not up yet?

I think we can meet both cases, my dogs as exemple never had passed bonitation in their life because its simply impossible by now so they will have this data empty untill I do it with then.
I think that if I dont do it with the acnoledge of the club, and with a judge accepted by the slovak or czech club, this bonitation will not be valid, and will show like an X in the database.
So, all dogs with X in the database are dogs with not recognized bontiations.
Maybe and not all times you also can meet some dogs that still don't have the results published, because the bonitation was so recently and admin didn't had time for do it yet.

And also it seems like there are many dogs with no HD info either. Once again, have they simply not been tested or more likely have the results not been sent in for it to show up here?

Well, there you can see some different cases:
1- Dogs that didn't reach the minimal age for make the HD and ED results, minimal age that will depend of the country rule.
For some countries the result can be done with 12 months, I find it a mistake because it didn't select, some others the minimal age is 15, its already ok but I dont believe much in these results, on others countries the results are made with 18, these are ok, they can change a little but are rare the cases that it happened, and with 24 months, that its the most correct.
Anyway, with 18 months its already ok, its 95,5% of the results be right, normally those 4,5% of changes are more common in molossers.
So, you need see if the dog have the correct age and so evaluate if he was suppose to have the HD and ED results or not.

2- Some cases of people which evaluate the dog, but the results are not good and so they decide to don't publish it.

3- Some people have do the results in the correct age, but their country are too burocratic that the return of the result is really slow, in my country it can arrive to one period of 1 year waiting the oficial paper, my luck is that they had published it online in german shepherd club because of a mistake in the breed cadastre.

Because I thought I read somewhere that litters from dogs with no HD or bonitation codes wouldn't be listed, but I see many litters of that sort listed.

The database is actualized time to time, but seems that the add of the litters is independnt of the actualization of the database, so, sometimes teh breeder had sent the results to the admin, the results are known but the database was not actualized, so the litter will be announciate without the HD and ED untill the database be actualized.