Possible Clues:

• Classification suggested by the beginning of 17-, 25-, 37- and 53-Across
• O for one damned exercise that involves little time
• AB positive, for example
• B+ or A-
• A family link to brand?
• Composed by old poet, characteristic of what comes from the heart
• 'A' might be a vampire
• A or B, for example?
• A definition of circulation given by old poet, perhaps?
• A+ or B-