The unfamiliar ingredient list

The recipe booklet had been assembled from handwritten contributions. One used a mug as a measure without giving its capacity. Another gave an oven temperature but did not say which scale it used. Two ingredients appeared in the instructions but not in the shopping list. A contributor had written 'cook until ready' beside a dish none of us had made before. We tried contacting the cooks, but several had already left for the holidays. Printing had been booked for Friday, leaving only one afternoon to test any corrected instructions.

Describe the difficulties of making the recipe booklet reliable. You may support your points with brief quotations.