Established since...
Established in Australia since 1965, the HSBC Group has a network ...reads a booklet I received today. It's lucky I don't choose my bank based on its use of English. The word since means 'during the period following', such as 'I lost my watch last Wednesday, and have not seen it since'. Their sentence implies that HSBC was established at some time following 1965, but they're not sure when.
Sometimes misuses like this can be justified as archaic, slang, or just rare. Unfortunately for HSBC, there are no alternative uses for since that fulfill any of these - see Google's dictionary source for a list.