The "J16" is not mentioned in any catalog or part list to my knowledge. Junghans documents only show that it had an internal used name J14 and it was sold to Alpina which named it Alpina 225. Alpina only got movments with a detached escape-wheel cock which would make it a J16/1.
The J16 can be found with two different used clicksprings.
It seems that the J16 was sold in Italy as "Chronometre-Junghans".
Above the newer type click spring.
TEXT FROM THE BOOKLET
CHRONOMETETRE JUNGHANSHIGH PRECISION WATCHGrand Prix Paris 1900Turin Grand Prix 1911
Special Medal of the Ministry of J. & C.Notes on the "Chronomètre Junghans" which are of interest only to professional(see below). F. BERARDI & C. - MILANwatchmakers and to which they are exclusively dedicated.The perfect watchmaker loves to examine the caliber meticulously, the first basis for themanufacture of a truly precision watch ....…. and he notes that in its construction everything has been thought of,taking advantage of the experiences and practice of years and years.CHRONOMÈTREThe etymology of the word chronometer, as everyone knows, is measure of time.But the professional of the noble and difficult art of the watchmakergives the honor to carry that name only to watches that measure it exactly.The name of the manufacturer JUNGHANS and the brand "STELLA" that distinguishthis watch are a proof of its perfect and constant accuracy."JUNGHANS"Who does not know by now this great HOUSE whose trademark for about 12 decadeshas established itself in the world market?Its magnificent known installations, are appreciated and taken for example bythe technicians allow them to carry out all the watchmaking worksfrom the rough to the smallest finishing accessory.INTERCHANGEABILITYAnd here is how built from the beginning with materials of the highest quality,with tools equipped with the latest refinements of fine mechanics and withthe system of absolute interchangeability, this watch givesprecision to be placed in the first rank of the best brands known so far.such guarantees of solidity, accuracy of manufacture and highThe pieces that compose it:All the supplies used are of the highest quality and have mathematically correct and controlled proportions.Pinions are not made of drawn steel but are mechanically cut into round steel.The wheels are cut with very precise automatic machines that guarantee a perfect gear.Rubies. The factory pays special attention to the choice of rubies it uses in its watches.The stones are of beautiful quality: Holes are of perfect regularity and polished with great care.The escapement has a fixed anchor, straight line, visible levers, double plateau and helipses in ruby.All pieces conform to the principle of theory.The balance wheel is made of two metals, it is carefully balanced, cut and controlled to offer a minimum of variation.The BREGUET spirals are of excellent steel treated with special temper.CONTROL:They are manufactured in real nickel 19''' and in silver 18''' and 19 1/2'''JUNGHANS watches are set flat, suspended, in scorching and freezing temperatures.Nikel 19''' Silver 19 1/2''' Deposit at:EMILIO STEFFANUTTI ~ MILANO (7) 66, Via Torino - Telephone 81-43The "CHRONOMETRE JUNGHANS" factory
Below a comparison of the J13, J15, J16 and J17.