If you aggregate the bond returns all of countries and ‘invest’ in that return series, almost certaintly your backtest will stop at some point because you will lose 100%.
Even if somehow you don’t, you will be hit with several 90-99% real return drawdowns (with no offsetting big gains like usually happens in stocks), which calls into question in how one should invest in that asset class in the first place. It’s very difficult to produce a positive return after losing such huge amounts….