Magnetic tape cartridge group and magnetic recording and reproducing device

A magnetic tape cartridge group comprising:

• a plurality of magnetic tape cartridges in which a magnetic tape is wound around a cartridge reel and accommodated in the magnetic tape cartridge,
• wherein the magnetic tape includes a non-magnetic support, and a magnetic layer containing a ferromagnetic powder,
• the magnetic layer includes a plurality of servo bands,
• regarding 100 reels of magnetic tape cartridges in the magnetic tape cartridge group, in a case where storage in an environment of a temperature of 23° C. and relative humidity of 50% for 12 hours and storage in an environment of a temperature of 32° C. and relative humidity of 55% for 12 hours are defined as one cycle, a maximum value of an absolute value of a difference between a servo band spacing obtained before the storage and a servo band spacing obtained after the storage of N cycles is defined as A, a unit of A is um, and N is set to 1, 2, 3, 4, or 5, an arithmetic mean of medium lives calculated by a linear function of A and a logarithm logeT of T, that are derived from a value of A and a value of the logarithm logeT of total storage time T of the storage of N cycles is 3 years or longer, and 3σ is 1 year or shorter, where σ is a standard deviation of the medium lives of the 100 reels of the magnetic tape cartridges,
• the medium life is T, in a case where A satisfies Equation a:
• A=1.5−B, and (Equation a)
• the B is a value calculated by multiplying a difference between a maximum value and a minimum value of servo band spacings obtained
• in each of the following five environments of
• a temperature of 16° C. and relative humidity of 20%,
• a temperature of 16° C. and relative humidity of 80%,
• a temperature of 26° C. and relative humidity of 80%,
• a temperature of 32° C. and relative humidity of 20%, and
• a temperature of 32° C. and relative humidity of 55%,
• by ½, and a unit is μm;
• and
• wherein
• (i) the magnetic layer comprises a compound having a polyalkyleneimine chain and a vinyl polymer chain;
• (ii) the magnetic tape further includes a back coating layer containing a non-magnetic powder on a surface side of the non-magnetic support opposite to a surface side provided with the magnetic layer, and
• the back coating layer comprises a compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1:
• in Formula 1, R represents an alkyl group having 7 or more carbon atoms or a fluorinated alkyl group having 7 or more carbon atoms, and Z+ represents an ammonium cation;
• and
• (iii) the magnetic tape is wound around a reel hub of the cartridge reel, and
• a bending elastic modulus of a material constituting at least an outer peripheral side surface layer portion of the reel hub is 5 GPa or more.