Quantities are important. A set of 100 samples is vastly preferable to a set of 10, and single samples are to be avoided except in desperation. One cannot tell from internal evidence whether a single sample has been re-used from an earlier construction, cut particularly for the purpose to which it was finally put, or is some later repair. Species are important. Oak, pine, juniper, fir, boxwood, yew, spruce, and occasionally chestnut have been crossdated.
Olive is hopeless, as are willow, poplar, and fruit trees.
Large rings in these genera may mean merely that the gardener in the orchards in which they grew was unusually industrious that year. Cypress is usually undatable because the latewood cannot easily be distinguished from an individual annual ring. Finally, the condition of the sample is important. If the bark is present, the precise felling year may sometimes be determined. If some sapwood rings are present, only an estimate of the felling date may be made.