Helen, don't worry about the comment you quoted. In the case of 3,3'-diethylthiatricarbocyanine, the spectral sensitivity shifts towards shorter wavelength side and best sensitivity is between 750 and 800nm. This dye works well with bromide emulsions with varying iodide content, as well as various core-shell structures (although there are preferred crystal designs, the preferred form is not too dissimilar to other dyes anyway).
J-aggregate is largely irrelevant in infrared sensitization because very low dye density is chosen. J-aggregate is used when sharp tuning (sharp cutoff) of spectral sensitivity is necessary, such as multilayer color films and modern multigrade papers.
The mechanism of spectral sensitization (and desensitization) has been elucidated quite well in the past decade, and a lot of old theories are now obsolete. It is very nice to be able to get rid of old empirical rules that don't always work and replace them with a few simple physical and chemical principles that explain all known issues that had not been explained before. This is the exciting time to understand sensitivity mechanisms of silver halide media, but like anything, it is necessary to have good background in solid state physics (semiconductor materials) and organic chemistry. Tani's book is excellent on this topic, and many conjectures he stated therein were actually later figured out by himself. But again, as you mentioned, the prerequisite to understand this topic (that is, his book) is not that modest.
When you take spectral sensitivity measured with chloride emulsions and try to infer it to bromide system, there is one issue that needs attention. Some dyes sensitize chloride emulsions but desensitize bromide emulsions. Good dyes that are used in modern practice generally don't have this sort of problems, but historical ones such as erythrosin can sensitize chloride emulsions decently, but it is impractical for bromide system. In this particular case, erythrosin adds a bit of green sensitivity but depresses the intrinsic sensitivity to blue light. Other than this, gross features of the dye rarely change drastically between chloride and bromide emulsions.