Would be decided on a case-by-case basis by the courts.
The primary element of a contract is a "meeting of minds". So the relevant questions would be "what did Bob intend to do?", "what did Alice intend to do?" and "do their respective intents create an agreement?"
Depending on what exactly was truncated, it may or may not affect the contract. There have been cases where the court decided that a contract different from the written contract signed by both parties had been formed, because it was clear that their agreement and what they wrote down was different and their intent trumped the written document.(1)
So only if the truncated parts would considerably change the intended contract is there a problem. If the truncated parts are standard contract boilerplate stuff that a reasonable person would expect to be part of a contract, it would likely be upheld by a court.
Of course, in practical terms, intent is difficult to prove if one or both parties are not cooperative. That's a whole other can of worms.
(1) This was a case between two merchants and a buying contract of a few tons of a specific type of fish from Norway. They wrote what they thought was the norwegian name for that fish on the contract, but mixed it up. When a container full of the wrong fish arrived, the buyer said "I didn't buy that" and the seller said "true, but it's what you signed so sorry the mistake is on you and you have to pay it". Both sides agreed that they had made a mistake and had originally intended to trade a different fish. The case was essentially over who would have to pay for the mistake. The court decided that the contract was for the intended fish, not the one written down.