英文時態的問題

IN the latest Audit Report, which came out last week, the Hong Kong Chinese Orchestra (HKCO) is criticized for its poor management. For example, its managers upgraded their travel and accommodation arrangements when the orchestra was on tour; some of its musicians have worked fewer hours than they ought to have under their contracts; and part of its box office income has actually come from its own purse because it has bought tickets, which it has given away.

1) 上面第一句的is criticized可唔可以用was criticized，因為佢講係上星期的report唔係應該過去了要用過去式?
2)some of its musicians have worked fewer hours......﹔part of its box office income has actually come from...... ，點解呢度用have worked唔用worked，有咩分別?另外個句的問題一樣。
我明白各動詞的基本用法，但在文章上時常都想不通點解，有什麼方法可以幫我
?