#the pragmatic solution would have been to put henry to oath with witnesses that mary would be first in succession after any sons

[fideidefenswhore]

How do we know that COA was offered her daughter made bona fides and kept princess? When was this?

It was an offer made by Henry alongside Campeggio when he was there before the trial, that her acceptance of the offer meant the trial could be foregone ....

We (Wolsey and Campeggio) are agreed in opinion to test the mind of the Queen, and to persuade her to consent to the separation, and to enter the profession of some religion. For this purpose his Lordship promised me the assistance of himself and all the prelates of the kingdom, and the favor of the King, and that the Queen shall have any honorable conditions which she demands, retain her station as Queen*, and not lose anything except "l'uso della persona del Re," which he (Wolsey) says she has lost for many years; allowing her her dowry, rents, ornaments, and assignments for her support, and many other things; especially that the succession of the kingdom for the present shall be established in her daughter, by the ordinance and consent of all the estates, in case there should never be any legitimate male heir. 

....(although, actually I don't exactly remember, that might have just been one stage of the offer...another might have been that her absence from the trial would ensure a result in Henry's favor; as we know she refused to attend after her speech and it did not, so whether or not that was true...Campeggio had a decretal comission to declare the marriage valid or invalid at Blackfriars and didn't, so in some sense they both got played, although Catherine only in hindsight...ironically, she would later vehemently complain about the severe injustice of the delay in any resolution, but she was the one that had interceded for that delay**, demanding the case only be tried in Rome). Even her counsel at the time, before becoming as contumacious as he did (Bishop Fisher), advised her to take this 'deal', as it were. Off the cuff, I don't remember every reference made to it, Chapuys some months later does also mention (very conditional) 'offers' made to her, but the dispatch is frustratingly vague:

Meanwhile the Queen is daily assailed by people making her all manner of offers, if she will only consent to the divorce; but she remains as firm as ever [...]

In 1533 Chapuys reports Catherine as having said she was willing to take the 'offer' made to her by the King's council three years ago, that then she had thought it was a feint to induce her to accept demotion, but she would accept it now. He does not specify what this offer was, I remember I went back to the sources of when Henry's council visited and argued with her and it was not clear then, either, but I always wondered if that was what she was alluding to. If so it was too late at that point; Henry had decided that the issue of any union that contravened divine law was irrevocably illegitimate (although technically, he would not manage to garner Parliamentary assent for this notion until three years later, he only managed it by implication in 1534), and he believed that was what it was.

Often apologia of Catherine's stance in the late 1520s has been, why should she have even considered that inducement, how was it even presented as an 'offer', even if the papacy had annulled the marriage, Mary would be bona fides regardless, etc. It was presented as an offer, inducement, compromise of sorts because in England that was not the legal precedent (ie, an offer made on behalf of her daughter that was not guaranteed otherwise):

"[Henry VIII] now argued she would would be barred by illegitimacy. This contention puzzled continental contemporaries because elsewhere in western Europe those children born to couples who in good faith believed themselves validly married were treated as legitimate. Nevertheless, Henry was right. After a period of some uncertainty, by the late fourteenth century England had opted out of the bona fides principle. As Sir John Baker notes, 'succession problems were usually debated in legal terms and in accordance with the common law canons of inheritance.' A successful challenge to his marriage would thus automatically bastardise Mary and leave Henry no direct heir... [although] Mary could have been legitimated by statute." - JF Hadwin, The Journal of Ecclesiastical History

*One assumes this meant only a ceremonial title of some sort, ie Dowager Queen of England, as her sister-in-law was still referred to as Queen of France.

**Probably not anticipating resolution would not take place for another four years, but...still.