I’m going to read the rest of your comment, but before I do I intend to clarify the part of my method that makes this particular situation you’re predicting very difficult:
When we are visualizing out “dance” in the grocery store, which brands of bread catch fire first? Does it start from the bottom? Which brands are down there ? Does it start from the top, like someone poured gasoline and flicked the match up top? Where exactly does the match land? Where exactly are we standing when we do our dance?
Which loaf of bread catches fire?
What is the bread next to? Is there anyone else in the aisle? Do we, the badasses that we are, care that others are around?
These are simple questions that cannot be answered without being there, in the store, at the bread aisle.
If you grab the bread and forget to check it off, it won’t matter. You have the bread. Leave the matches for another day.
Okay, on to the rest.
Edit:
you wrote:
The first accidental meeting of mr. Gray in combination with the conscious effort to memorize him could have altered the archetypical going to the supermarket story in that he is now a to be expected part of that story. So in the 4 times supermarket adventures after meeting him he is not just included in the memory, but so is my logically to be expected reaction to that inclusion.
This makes sense.
Perhaps I don’t see “is this real” as a particular issue because I have memorized and reorganized and rememorized/overwritten a lot of information.
The distinguishing feature of which imagery is the “real” imagery is to incorporate a unique identifier that simply cannot be purely-imagined.
Maybe it’s just me, but I find this task very simple and closing in on nigh automatic.
Also, I specifically limit myself from certain forms of “previsualizing” purposely to avoid confusing myself later. Because I really agree with you. I think we can totally “previsualize” and believe it as reality.
My recommendation is: Don’t do that. 

Edit #2:
I really like your points, @erikfromholland as they’re good clarifying questions for me to think about.
After some more thought, I recognized a “rule” I have for To-do lists and I’d forgotten why I followed the rule so I forgot the “rule” existed or that I’d made a decision in the first place and now it’s just a convention of habit:
Rule: Don’t memorize To-Dos in the same place they need to be To-Done.
That is, don’t place a memorized a grocery list in the grocery store. Don’t place a memorized list of household chores in the house. Don’t place memorized directions in whatever mode of transportation will be taken (car, bus, walk, train, etc).
Something about the bread burning scenario seemed “off” to me. But I couldn’t place it at first. Sitting down thinking about it I wondered to myself, “why would I memorize bread burning in the grocery store?”
That’s when I realized: I wouldn’t. I don’t put task lists in domain-related areas. It will naturally make everything more confusing.
I might memorize the grocery list outside my house. Or on my arms. Or even with martial art techniques (I’ve tried it, it’s tough). But never actually in a grocery store. Too much potential confabulation. I totally agree.