Since there are contemporary records for there being two separate attacks, there's no doubt that there were two.The problem is with the attack on 15 May 1789. The contemporary account of this only identifies the attack as being against "Mr Wallen". nor makes any mention of his wife, much less about her being wounded. It is the quote from Addington, based on a letter of Thomas W. Carter's letter in the Draper Msc, that associates it with John Wallen, and provides the information about his wife being wounded.
Thomas Carter was not a contemporary of this event, and only knew of the attack second or third hand. From researching other problems I find Carter's information is sometimes reasonably accurate, but sometimes its quite wrong (Draper's marginalia on the letter show that he himself questioned some of Carter's information).There are instances where Carter has clearly combined elements of different stories to make a single story which he presents to Draper.
Do you know of anything other than Addington's quote of the Thomas Carter letter that associates John Wallen with the attack on 15 May 1789?