1 - you need to be careful with words - I believe you are using album when you mean event - there is a major difference -- going through your post as posted
I have say 300 pics in a folder called "Holiday snaps from camera" in my desktop.
OK
I import them to iphoto and create an album - call it "holidays"
Importing the photos typoically does not create an album (although it is possible) - it creates one or more events - typically you then create albums which may or may not include all of those photos
I trash the " holidays" album totally
Now the album you created is gone but the underlying photos are still in their events
I then go back to desktop " Holiday snaps from camera" and delete some of them and rearange them so now I have 250 pics.
Ok - this has no effect on iPhoto in anyway
I import them in iphoto and create another album called "holiday snaps final"
and again Importing the photos typically does not create an album (although it is possible) - it creates one or more events - typically you then create albums which may or may not include all of those photos - doing exactly what you say you now have one album "holiday snaps final" with 250 photos and 550 photos (300 from the first import and 250 from the second import) in two or more events
If i then go to iphoto trash and trash the original album " holidays" - will that also trash my newly created album "holiday snaps final" which contains all the same photos?
No as stated many time in answering you, there is no connection - each photo is in the library and can be viewed several ways - and deleting albums does not affect photos in the library - it simply removes the album and has no effect on the photo its self - each import creates new event(s) which have no connection to any previous event
We are still in the same loop going through the same questions over and over and over
Your total confusion may be a result of calling event albums - which they are not - albums and events operate totally differently - deleting a photo form an album has not effect on the photo anywhere - it just removes it form the album and nothing going into the trash - deleting from an event does totally delete the photo everywhere in i{Photo and does put the photo in the iPhoto trash - once you empty the iPhoto trash that photo is gone - everywhere - duplicates of it or different photos in other events are not affected in any way - only the photo you delete is deleted
I think an iPhoto class would be a giant help to you - you do not understand how iPhoto works - even the tutorials will help some if you become specific on your language - http://www.apple.com/support/iphoto/
LN