Vintage Tiger 07 955i Fresh Oil Level

Im sure someone has discussed this but I cant find a specific answer on oil change levels/qty for the 955i tiger !
Now this is my first Triumph an 07 with only 10k, have done a few of the common mods to it already and she's a beaut but I am still learning about their foibles and the triple engine. So to oil....
Thorough heat up and drain down, even leaning it to get dregs out. New filter pre-filled and oil topped up with a touch under 4 litres as per manual and handbook. Start engine and run for a few minutes, stop and leave for about 15. Check level with dipstick screwed in, level on wheels, too much oil. Had to draw out about 1/2 litre to get level correct. !!?? This is my first oil change since buying, but previous owner had also overfilled it (but not ridden it after) and I couldn't figure how or why when I corrected it !
Now why does it seem to take less oil than the manuals !? or am I missing something obvious ?
I have always serviced my own bikes and am very careful to get things right - Guzzi oil levels are interesting too !
hopefully someone can shed a bit of oil light here ?

thanks H

 

Thanks for the replies - I would rather trust the dipstick rather than what goes in but manual does say 4lt empty filter and 4.3lt with prefilled filter ! I just wondered if some old oil hid away somewhere like the gearbox !?
A mystery but ok I guess