AFAIK the ASH credit is used only in US productions.

Spooks is a British show that doesn't have any credits, the credit is most likely taken from the facts files on the DVD, but I doubt he is listed as ASH there.

Personally, I would use ASH, because Buffy is (and probably will be) his most prominent credit, but the CLT points toward AH, so that should probably be used for contributions.

That's the way I understand it as well. He uses ASH in the US (maybe there's another Anthony Head in SAG?) and AH in the UK.
Obviously when we're just talking about films decoding the CLT is relatively easy, but how should we take into account TV series, do we count it as only 1 title, or each season as a title, or some other way?

My personal opinion is that each unique name for an actor in a TV series should count as an entry.

For example, for the first few seasons of Star Trek Deep Space Nine, Alexander Siddig was credited as Siddig El Fadil. Following my opinion, each of those would count as 1 entry for each variation of the name.

As I said though, that is only my opinion & not necessarily the official way to do things. As there's nothing (that I could see) in the rules about the CLT & TV series, it's probably every entry counts as one.

Just thinking about something that applies to this kind of situation... I've also run across crew credits (at least) where the name changes within a season as well.

A couple of months ago, I did a full audit for the early 90's series of Dark Shadows.

Sound Re-Recording Mixer Edward F. Suski worked on episodes 2-12.

For episodes 2 & 3, he's credited as Ed Suski, and then from episodes 4-12 he's credited as Edward F. Suski.

BOTH credits would legitimately be counted, would they not? Even though they come from the same season? They're both counted in the CLT results. (I used common name of Edward F. Suski at the time, because even though Ed Suski comes out higher in the CLT counts, he's got about 18 credits that all fall under the same variation of three television series... so at the time I guess I was only counting those as one unique entry each, although with this discussion, that might not hold up anymore...).

I know I've run into the problem on more than one occasion as well. Also recently submitted a new Canadian Locality profile for Popular Season One.

In that season, there's a sound crew member that's credited two different ways in the 22 episodes, and had a common name different to both credits (can't remember if he was actually credited under the common name though).

So really, when you think about it, there are CLT counts that actually break down into almost Eposidic numbers even though the CLT doesn't reflect that (as it only counts titles which would contain the specific episodes).

It would be interestiing to know if it counts number of credits or just titles.  I used the CLT to look up Alexander Siddig and, if you click on one of the DS9 credits, he is listed multiple times.  Whether or not all those are counted is the question.

Even my Buffy profiles uses Anthony Head as the common name...

Definitely Anthony Head. There are a HUGE numbers of different titles in which he's credited as such, and only a very few credits as Anthony Stewart Head. The lists shown in the original post are very clear. Additionally - not that it really matters for our purposes, but still interesting to note - his official website confirms that's what he chooses to go by.

Following Kluge's suggestion I've split Buffy into seasonal titles, but to be fair I've done the same to Little Britain.
I still think the AH title list could end up bigger than the ASH list. The problem is because of the way we enter TV series into the database, each individual profile is counted as a separate title. So a 6 disc season boxset would count to the CLT as 7 separate entries.

Also, should we count episode compilation discs as separate titles or as part of the TV series?