Capellanus also is the first source I have encounter for the "base" system: the division of the advance of Love's player on the corners of the baseball diamond. He, of course, doesn't mention the game itself, but he does say that "[f]rom ancient times four distinct stages have been established in love: the first consists in the giving of hope, the second in the granting of a kiss, the third in the enjoyment of an embrace, and the fourth culminates in the yielding of the whole person." I was never quite clear what second and third were, but now I have a 12th century authority.
The Art of Courtly Love's worth reading just for the odd power system it espouses, in which the lover must do whatever his beloved--or indeed any woman--commands, and the woman is free to choose whichever lover she finds most admirable; but she must choose. A woman who never chooses a lover is, in one elaborate allegory designed to unlace a pretty bodice, doomed in a strange afterlife to wear fox skins in burning heat while riding in Love's train, then to sit upon thorns and been jounced by men much to her discomfort. Whereas a woman who takes a lover may therefore much improve him, and thereby win great renown. It's a strange book, and even as exaggeration points to a perturbed state of things. I shall close with Love's rules, as won by an unnamed knight (I think Lancelot) from King Arthur's court.
I. Marriage is no real excuse for not loving.
II. He who is not jealous cannot love.
III. No one can be bound by a double love.
IV. It is well known that love is always increasing or decreasing.
V. That which a lover takes against his will of his beloved has no relish.
VI. Boys do not love until they arrive at the age of maturity.
VII. When one lover dies, a widowhood of two years is required of the survivor.
VIII. No one should be deprived of love without the very best of reasons.
IX. No one can love unless he is impelled by the persuasion of love.
X. Love is always a stranger in the home of avarice.
XI. It is not proper to love any woman whom one should be ashamed to seek to marry.
XII. A true lover does not desire to embrace in love anyone except his beloved.
XIII. When made public love rarely endures.
XIV. The easy attainment of love makes it of little value; difficulty of attainment makes it prized.
XV. Every lover regularly turns pale in the presence of his beloved.
XVI. When a lover suddenly catches sight of his beloved his heart palpitates.
XVII. A new love puts to flight an old one.
XVIII. Good character alone makes any man worthy of love.
XIX. If love diminishes, it quickly fails and rarely revives.
XX. A man in love is always apprehensive.
XXI. Real jealousy always increases the feeling of love.
XXII. Jealousy, and therefore love, are increased when one suspects his beloved.
XXIII. He whom the thought of love vexes, eats and sleeps very little.
XXIV. Every act of a lover ends with in the thought of his beloved.
XXV. A true lover considers nothing good except what he thinks will please his beloved.
XXVI. Love can deny nothing to love.
XXVII. A lover can never have enough of the solaces of his beloved.
XXVIII. A slight presumption causes a lover to suspect his beloved.
XXIX. A man who is vexed by too much passion usually does not love.
XXX. A true lover is constantly and without intermission possessed by the thought of his beloved.
XXXI. Nothing forbids one woman being loved by two men or one man by two women.