Spot rate and BEY question, problems, sometimes, like

edgeon

Hopefully this is a simple question - but I feel like I keep running into problems when either valuing a bond or doing arbitrage where sometimes the spot rate given needs to be divided by 2 and sometimes it needs to be left alone for discounting.

Does it have to do with the BEY? Or should the spot rate always be divided by 2 in all cases?

Thanks.