From Duolingo:

"SHORT PARTICIPLES

Passive participles can be short, like adjectives, which is most useful for past participles. The agent, if needed, is in the Instrumental (such a use sounds quite formal):

Пла́тье (бы́ло) сде́лано в Кита́е. = The dress was made in China.
Э́та кни́га (была́) напи́сана в 1999 = This book was written in 1999.
Иллюстрация нарисована мной. = The illustration was drawn by me."

So with short form adjectives denoting temporary states "Он голоден" and short form past participles denoting the passive "книга написана в 2016" it gets a little confusing.

Then at the end of another website it gave an example which further confused matters:

"Here are some examples of past passive participles from some common verbs. Note that you can use the past and future of быть with these participles, just as you can with other short adjectives (like Она была/будет больна):
Сказано — сделано! No sooner said than done! (a saying)
Магазин закрыт на ремонт. Store closed for renovations. (a sign)
Все приглашены. Everybody has been invited.
Всё было сделано вовремя. Everything was done on time."

Surely as stated in the duolingo lesson, if it is infact a past participle then the past is implied, along with the (был/а/о). With words like больна and закрыт, wouldn't these be considered pure adjectives, as you can use them with no implication of the past (or of any action atall, merely a state in the present)?

Is it fair to say that these pure adjective have been constructed from past participles but now have a status of an adjective? As I imagine there are past participles that could not be used in the same manner as закрыт, for example написана would always imply the "была" in my mind, therefore cannot be considered an adjective.

Likewise I imagine without the status of full adjective you could not use it as a predicate: летящая птица but not птица летящая (unless inverting the words for stylistic reasons). You would surely have to use птица летит.

Just putting my thoughts out there as I saw the old сломан and thought to myself, are russians seeing (был) сломан (it was broken) and then inferring it must be broken in the present, or like in english, have the word "broken" got the status of full adjective and has gained meaning beyond its use as a past participle?

Sorry if this is confusing, but I'm trying to unwrap it in my own mind as well,

Cheers, Jake.