basically it is just Vientiane and Savannakhet that got strict on visa applicaions. I frequently look at the online system of KL and you can even get slots for the same day. Looks like they are very reasonable.
Benjamin Hays on that I have to correct, Cambodia Airport not allow same day OUT/IN. They request 24 hours in country. At land border they ask a small service fee to forget that requirement.
only the land border count will reset on 1.1.2020. They write manually
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or this year
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. No rule re Tourist, when the Thai Embassy in Vientiane changed that "Lady" was heard shouting "ONE PER YEAR", but this is no rule. Without a remark you could apply for a second within same year, but if they approve is a different story.
there are always ways to beat the system. If you in UK try to get a SETV or METV. If you have a past history avoid entry via airport, extend. Than do 2 border run in one year. Take a look at the calendar, we already in September, if you plan ahead you can stay at least 8 -14 month without worry.