Grammar !!

一句唔可以有兩個verb，係指唔可以有兩個verb表達同一個tense。如：
He goes to swims at 3pm.
現在式第三身單數，第一個（去一個地方）係動詞，s 加o係 go 度，第二個唔係叫做動詞，而係 to infinitive，必須跟住 to。只有can / could / will / would / shall / should / may / might / must 呢ｄ modal verbs後先會跟動詞而冇 to o係中間。
然後呢，唔好睇 I were swimming 住，睇 I am swimming 先。am swimming / is swimming / are swimming 加埋先係一個 tense（present continuous）。係唔係？咁 I were swimming 裏面，were swimming 亦係加埋先係一個 tense（past continuous）。有Ｄ tenses 係要多個一個字先表達到時態（如 present perfect：have/has+past participle，past perfect：had+past participle等）。
至於 So some of our target market was overlapped，其實你有學過 passive voice？你呢句就係，但凡句子be (=is/am/are/was/were/been)+past participle，都係passive voice（在此且不深究）。
例如：The cake was eaten by me.
意思係「件蛋糕俾係我食左」，但咁係乜野tense？其實只係 simple past tense，因為用active voice寫返原句，係：
I ate the cake.
將句字中 main verb（話你知做左ｄ乜o個個verb）變成 past participle 只係 passive voice o既句式，主／被動講緊同一件事，tense點會唔同？
返去你o個句：So some of our target market was overlapped，其實講tense o既只係 was，即 simple past。但呢句其實有ｄ錯，因為根本應該用 active voice 去寫（Some of our target marketS overlapped. 有ｄ目標市場重覆左。邊個令佢地重覆？睇唔到，冇資料。除非係人為引致呢個情況，否則如此寫法即可）。但係呢度旨在話你知呢個句式係passive voice，與tense冇關。