use a countable noun to represent a category

[Uktous]

hi,

based on the following 3 sentences, is my logic correct?

sentence1:
thank you for applying for our accounting vacancy
logic:
(the word vacancy represents all accounting vacancies in his firm)

sentence 2:
thank you for applying for our 2010 Graduate Vacancy
logic:
(the word vacancy represents all graduate vacancies in 2010 in his firm)

sentence3:
our 2010 entry holds both accounting and computing vacancies
logic:
(the word vacanies represent all accouting vacancies and all computing vacancies)

[Cerberus™]

In the first two sentences, it says "vacancy" singular, so I'd take it as just one job in each; in the last sentence, any combination of single and multiple jobs for each department is theoretically possible.