1) What paper/TV company are you working for?
2) I assume you are looking at if there is any difference in the two engine configuratuions on the 146 to RJ? The ALF502 and 507?
3) Read the SB that you are trying to interpret with clearly no technical training. As stated above, it will specify the Serial Numbers of the affected aircraft OR as in this case ALL BAe 146 aircraft.
4 As its an ISB its an INSPECTION SB so no doubt a follow up will be required and possible repeat inspections. I assume its the inspect the Air Conditioning Ducting for oil contamination inspection?